[PATCH v3 3/4] of_net: add mac-address-increment support

[Ansuel Smith <ansuelsmth@xxxxxxxxx>]

Lots of embedded devices use the mac-address of other interface
extracted from nvmem cells and increments it by one or two. Add two
bindings to integrate this and directly use the right mac-address for
the interface. Some example are some routers that use the gmac
mac-address stored in the art partition and increments it by one for the
wifi. mac-address-increment-byte bindings is used to tell what byte of
the mac-address has to be increased (if not defined the last byte is
increased) and mac-address-increment tells how much the byte decided
early has to be increased.

Signed-off-by: Ansuel Smith <ansuelsmth@xxxxxxxxx>
---
 drivers/of/of_net.c | 57 ++++++++++++++++++++++++++++++++++-----------
 1 file changed, 44 insertions(+), 13 deletions(-)

diff --git a/drivers/of/of_net.c b/drivers/of/of_net.c
index 6e411821583e..bafbc833e659 100644
--- a/drivers/of/of_net.c
+++ b/drivers/of/of_net.c
@@ -45,7 +45,7 @@ int of_get_phy_mode(struct device_node *np, phy_interface_t *interface)
 }
 EXPORT_SYMBOL_GPL(of_get_phy_mode);
 
-static const void *of_get_mac_addr(struct device_node *np, const char *name)
+static void *of_get_mac_addr(struct device_node *np, const char *name)
 {
 	struct property *pp = of_find_property(np, name, NULL);
 
@@ -54,26 +54,31 @@ static const void *of_get_mac_addr(struct device_node *np, const char *name)
 	return NULL;
 }
 
-static const void *of_get_mac_addr_nvmem(struct device_node *np)
+static void *of_get_mac_addr_nvmem(struct device_node *np, int *err)
 {
 	int ret;
-	const void *mac;
+	void *mac;
 	u8 nvmem_mac[ETH_ALEN];
 	struct platform_device *pdev = of_find_device_by_node(np);
 
-	if (!pdev)
-		return ERR_PTR(-ENODEV);
+	if (!pdev) {
+		*err = -ENODEV;
+		return NULL;
+	}
 
 	ret = nvmem_get_mac_address(&pdev->dev, &nvmem_mac);
 	if (ret) {
 		put_device(&pdev->dev);
-		return ERR_PTR(ret);
+		*err = ret;
+		return NULL;
 	}
 
 	mac = devm_kmemdup(&pdev->dev, nvmem_mac, ETH_ALEN, GFP_KERNEL);
 	put_device(&pdev->dev);
-	if (!mac)
-		return ERR_PTR(-ENOMEM);
+	if (!mac) {
+		*err = -ENOMEM;
+		return NULL;
+	}
 
 	return mac;
 }
@@ -98,24 +103,50 @@ static const void *of_get_mac_addr_nvmem(struct device_node *np)
  * this case, the real MAC is in 'local-mac-address', and 'mac-address' exists
  * but is all zeros.
  *
+ * DT can tell the system to increment the mac-address after is extracted by
+ * using:
+ * - mac-address-increment-byte to decide what byte to increase
+ *   (if not defined is increased the last byte)
+ * - mac-address-increment to decide how much to increase. The value will
+ *   not overflow to other bytes if the increment is over 255.
+ *   (example 00:01:02:03:04:ff + 1 == 00:01:02:03:04:00)
+ *
  * Return: Will be a valid pointer on success and ERR_PTR in case of error.
 */
 const void *of_get_mac_address(struct device_node *np)
 {
-	const void *addr;
+	u32 inc_idx, mac_inc;
+	int ret = 0;
+	u8 *addr;
+
+	/* Check first if the increment byte is present and valid.
+	 * If not set assume to increment the last byte if found.
+	 */
+	if (of_property_read_u32(np, "mac-address-increment-byte", &inc_idx))
+		inc_idx = 5;
+	if (inc_idx < 3 || inc_idx > 5)
+		return ERR_PTR(-EINVAL);
 
 	addr = of_get_mac_addr(np, "mac-address");
 	if (addr)
-		return addr;
+		goto found;
 
 	addr = of_get_mac_addr(np, "local-mac-address");
 	if (addr)
-		return addr;
+		goto found;
 
 	addr = of_get_mac_addr(np, "address");
 	if (addr)
-		return addr;
+		goto found;
+
+	addr = of_get_mac_addr_nvmem(np, &ret);
+	if (ret)
+		return ERR_PTR(ret);
+
+found:
+	if (!of_property_read_u32(np, "mac-address-increment", &mac_inc))
+		addr[inc_idx] += mac_inc;
 
-	return of_get_mac_addr_nvmem(np);
+	return addr;
 }
 EXPORT_SYMBOL(of_get_mac_address);
-- 
2.27.0